Answer
$[HBr] = 5.623 \times 10^{- 5}M$
Work Step by Step
1. Calculate the hydronium concentration:
$[H_3O^+] = 10^{-pH}$
$[H_3O^+] = 10^{- 4.25}$
$[H_3O^+] = 5.623 \times 10^{- 5}M$
2. Since $HBr$ is a strong acid: $[HBr] = [H_3O^+] = 5.623 \times 10^{- 5}M$
